Obesity is the most prevalent nutrition-related problem in the U.S.. About 20% of U.S. children are obese and the prevalence of obesity is increasing in both adults and children. Children suffer from many of the same obesity-related morbidities as adults: hypertension, dyslipidemia and insulin-resistance. In addition, obese children are frequently subjected to severe psychological stress from social stigmatization. Body fatness is a continuous quantitative trait reflecting the interaction of development, environment and genotype. Heritability of adipose tissue distribution, physical activity, resting metabolic rate and various aspects of feeding behavior are estimated to be 30-40%. Heritability of early onset obesity may be considerably higher than that for adult obesity. The aim of this study is to understand the molecular physiology of obesity in humans using candidate genes based mainly on rodent genetic models of obesity. The goal is to identify genes in which mutation and/or allelic variation in humans conveys susceptibility to obesity. Identification of these genes and their mechanism of action in human subjects will permit the rational subdivision of obesity into biologically meaningful subgroups which will, in turn, allow focused efforts to elucidate pathophysiology. The Children's Hospital of Philadelphia is one of several institutions from which samples are being collected for this study. To date eight children have been enrolled at Children's Hospital of Philadelphia. These subject samples have been sent to Columbia-Presbyterian to be added to the data pool. There have been no problems in the recruitment of subjects or the completion of the protocol. Subject enrollment will continue as described above.